According to example configurations herein, a clamp circuit includes: i) a power dissipation circuit disposed between a first node and a second node of the clamp circuit, and ii) a capacitive element disposed in a control path between the first node and a control input of the power dissipation circuit. During operation, when a voltage spike occurs at the first node, such as caused by opening of a respective switch, the capacitive element in the control path conveys a portion of energy from the first node to control activation of the power dissipation circuit. That is, during the voltage spike, based on conveyance of the energy over the control path, the power dissipation circuit turns ON to dissipate the transient voltage, protecting a main power switch.
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1. An apparatus comprising: a clamp circuit including a first clamp circuit node, a second clamp circuit node, a power dissipation circuit, a voltage-dependent circuit element, a capacitive element, and a discharge capacitor, wherein the power dissipation circuit includes a first resistor and a clamp switch, the clamp switch having a control input, the first resistor being serially connected to the clamp switch between the first clamp circuit node and the second clamp circuit node, wherein the voltage-dependent circuit element is connected to the first clamp circuit node, the voltage-dependent circuit element having an associated voltage threshold value, wherein the capacitive element is connected to the control input, the voltage-dependent circuit element being serially connected to the capacitive element in a control path between the first clamp circuit node and the control input, wherein the discharge resistor is connected between the control input and the second clamp circuit node, wherein the capacitive element is operative, in response to a transient voltage at the first clamp circuit node exceeding the voltage threshold value, to pass energy from the first clamp circuit node to the control input, thereby causing the clamp switch to operate in a saturation mode from a first time T 1 to a second time T 2 , and wherein the discharge resistor is operative to discharge the capacitive element from about the second time T 2 to a third time T 3 , thereby causing the clamp switch to operate in a linear mode from the second time T 2 to the third time T 3 ; a main over switch including a first power switch node and a second power switch node, the main power switch being disposed in a circuit path between the first power switch node and the second power switch node, the first clamp circuit node being electrically coupled to the first power switch node, the second clamp circuit node being electrically coupled to the second power switch node, the main power switch being operative, upon a selective activation of the main power switch, to switch between providing a high impedance and a low impedance on the circuit path between the first power switch node and the second power switch node; and a detector circuit operative to monitor a current conveyed on the circuit path through the main power switch, and to initiate opening of the main power switch depending upon a magnitude of the monitored current.
The apparatus protects a power switch from voltage spikes using a clamp circuit. The clamp circuit consists of a resistor and a switch (like a transistor) in series between two nodes, in parallel with the main power switch. A Zener diode (voltage-dependent element) is connected to one of the nodes. A capacitor and a discharge resistor control the transistor switch. When a voltage spike exceeds the Zener diode's threshold, the capacitor passes energy to the transistor's control input, turning it ON in saturation mode (T1 to T2). The discharge resistor then slowly turns the transistor OFF (linear mode from T2 to T3). A detector monitors the current through the main power switch and opens it if the current is too high, triggering this clamp circuit protection.
2. The apparatus as in claim 1 , wherein the voltage-dependent circuit element is a Zener diode.
The apparatus uses a Zener diode as the voltage-dependent circuit element in the clamp circuit. This Zener diode is connected to the main circuit node and activates the clamp circuit when the voltage exceeds the Zener diode's specific threshold voltage. The Zener diode protects the capacitive element from the full surge voltage. Otherwise, operation remains as defined in the main apparatus description.
3. The apparatus as in claim 1 , wherein the capacitive element is operative to limit a level of the transient voltage from the first clamp circuit node to the control input in order to control activation of the power dissipation circuit.
In the apparatus, the capacitor in the control path limits the voltage passed from the main circuit node to the control input of the power dissipation circuit. This voltage limiting action prevents overdriving the power dissipation circuit switch, controlling the point at which the clamp engages and protects the main power switch during a voltage spike. This improves switch reliability and ensures proper activation of the power dissipation circuit.
4. The apparatus as in claim 1 , wherein the capacitive element is further operative to pass the energy from the first clamp circuit node to the control input in order to control a conveyance of current from the first clamp circuit node to the second clamp circuit node.
The apparatus uses the capacitor in the control path to pass energy from the circuit node experiencing the voltage spike to the power dissipation circuit's control input. This capacitor-mediated energy transfer directly controls how much current flows through the power dissipation circuit, preventing excessive current from damaging the main power switch.
5. The apparatus as in claim 1 , wherein the capacitive element is further operative to pass the energy from the first clamp circuit node to the control input in order to control an amount of the energy applied to the control input of the clamp switch, and wherein, upon opening of the main power switch, each of the first resistor and the clamp switch is operative to dissipate power, the first resistor being operative to dissipate a larger proportion of the power than the clamp switch.
In the apparatus, the capacitor controls the energy applied to the power dissipation switch. When the main power switch opens, both the resistor and the switch in the power dissipation circuit dissipate power. The resistor is designed to dissipate the majority of this power, protecting the switch from overheating and potential damage. Operation is governed by the action of the capacitor.
6. The apparatus as in claim 1 , wherein the capacitive element is further operative to limit a level of the transient voltage from the first clamp circuit node to the control input of the clamp switch.
The apparatus utilizes the capacitor to limit the voltage of the transient signal that is passed from the high voltage point to the control input of the clamp switch. This prevents the transient high voltage from damaging the control input and ensures that the power dissipation element of the clamp is reliably activated.
7. The apparatus as in claim 1 , wherein the clamp switch is a metal oxide semiconductor field effect transistor (MOSFET) switch, wherein the MOSFET switch includes a gate node, a source node, and a drain node, wherein the gate node is the control input, wherein the source node is electrically connected to the second clamp circuit node, wherein the drain node is electrically connected to the first resistor, and wherein the discharge resistor is connected between the gate node of the MOSFET switch and the source node of the MOSFET switch.
The clamp switch in the apparatus is a MOSFET. The MOSFET's gate is the control input, its source is connected to the second clamp node, and its drain is connected to the resistor. The discharge resistor is connected between the MOSFET's gate and source. This configuration is used to control current flow during a transient overvoltage event.
8. A method of controlling a clamp circuit during a transient voltage condition, comprising: providing a clamp circuit including a first clamp circuit node, a second clamp circuit node, a power dissipation circuit, a voltage-dependent circuit element, a capacitive element, and a discharge capacitor, the power dissipation circuit including a first resistor and a clamp switch, the clamp switch having a control input, the first resistor being serially connected to the clamp switch between the first clamp circuit node and the second clamp circuit node, the voltage-dependent circuit element being connected to the first clamp circuit node, the voltage-dependent circuit element having an associated voltage threshold value, the capacitive element being connected to the control input, the voltage-dependent circuit element being serially connected to the capacitive element in a control path between the first clamp circuit node and the control input, and the discharge resistor being connected between the control input and the second clamp circuit node; in response to a transient voltage at the first clamp circuit node exceeding the voltage threshold value, passing, by the capacitive element, energy from the first clamp circuit node to the control input in order to cause the clamp switch to operate in a saturation mode from a first time T 1 to a second time T 2 ; discharging, by the discharge resistor, the capacitive element from about the second time T 2 to a third time T 3 in order to cause the clamp switch to operate in a linear mode from the second time T 2 to the third time T 3 ; providing a main power switch including a first power switch node and a second power switch node, the main power switch being disposed in a circuit path between the first power switch node and the second power switch node, the first clamp circuit node being electrically coupled to the first power switch node, the second clamp circuit node being electrically coupled to the second power switch node; upon a selective activation of the main power switch, switching, by the main power switch, between a first state of providing a high impedance and a second state of providing a low impedance on the circuit path between the first power switch node and the second power switch node; monitoring a current conveyed on the circuit path through the main power switch; and initiating opening of the main power switch depending upon a magnitude of the monitored current.
A method protects a power switch from voltage spikes using a clamp circuit. The clamp circuit contains a resistor and switch in series, with a Zener diode connected to one node. A capacitor and discharge resistor control the switch. If the voltage exceeds the Zener diode's threshold, the capacitor sends energy to the switch, turning it ON in saturation mode (T1 to T2). The discharge resistor then gradually turns the switch OFF (linear mode, T2 to T3). A main power switch selectively provides low or high impedance. Current through the main switch is monitored, and it's opened if the current is too high, initiating clamp circuit activation.
9. The method as in claim 8 further comprising: limiting, by the capacitive element, a level of voltage from the first clamp circuit node to the control input in order to control activation of the power dissipation circuit.
The method also includes limiting the voltage passed from the circuit node experiencing the spike to the power dissipation circuit's control input using the capacitor. This controls when the power dissipation circuit activates, protecting the main power switch from overvoltage and ensuring reliable operation. Operation remains as defined in the method description.
10. The method as in claim 9 further comprising: limiting, by the capacitive element, a level of the transient voltage from the first clamp circuit node to the control input of the clamp switch.
The method involves using the capacitor to limit the voltage of the transient signal that is passed from the high voltage point to the control input of the clamp switch. This specifically limits the *transient* voltage, preventing damage to the control input and ensuring reliable activation of the clamp's power dissipation element during these high-voltage events. Operation remains as defined in the method description.
11. The method as in claim 8 , wherein the clamp switch is a metal oxide semiconductor field effect transistor (MOSFET) switch, wherein the MOSFET switch includes a gate node, a source node, and a drain node, wherein the gate node is the control input, wherein the source node is electrically connected to the second clamp circuit node, wherein the drain node is electrically connected to the first resistor, and wherein the discharge resistor is connected between the gate node of the MOSFET switch and the source node of the MOSFET switch, and wherein the method further comprises: passing, by the capacitive element, the energy from the first clamp circuit node to the gate node of the MOSFET switch in order to control i) an activation of the MOSFET switch, and ii) a conveyance of current from the first clamp circuit node to the second clamp circuit node through the power dissipation circuit.
In the method, the clamp switch is a MOSFET, with the gate as the control input, source connected to the second clamp node, and drain connected to the resistor. The discharge resistor connects between the gate and source. The capacitor sends energy from the circuit node to the MOSFET's gate. This controls both the MOSFET's activation *and* the current flow through the power dissipation circuit from one node to the other, protecting the main power switch. Operation remains as defined in the method description.
12. The method as in claim 8 further comprising: controlling, by the capacitive element, an amount of the energy applied to the control input of the clamp switch; and upon opening of the main power switch, dissipating power by each of the first resistor and the clamp circuit, the first resistor dissipating a larger proportion of the power than the clamp switch.
The method involves controlling the energy applied to the clamp switch's control input using the capacitor. When the main power switch opens, both the resistor and switch dissipate power, with the resistor dissipating more power. This protects the switch from overheating and ensures a controlled power dissipation during the clamping process, mitigating voltage spikes. Operation remains as defined in the method description.
13. The method as in claim 8 further comprising: limiting, by the capacitive element, a level of the transient voltage from the first clamp circuit node to the control input of the clamp circuit.
The method involves using the capacitor to limit the transient voltage that is passed from the high voltage node to the control input of the clamp circuit. This protects the control input circuitry from potentially damaging voltage levels during transient events and ensures the clamp circuit operates reliably when needed. Operation remains as defined in the method description.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
May 27, 2015
March 14, 2017
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